The invention also relates to a method of manufacturing a semiconductor device comprising a semiconducting contact layer and a silicon oxide insulating layer which is located thereon and which has at least one aperture, as well as an electrode layer of platinum which is located on the insulating layer and which is in ohmic contact with the contact layer via said aperture and to such a semiconductor device, in particular a semiconductor laser.
Examples of the intended semiconductor devices are lasers, LEDs, integrated ferroelectric memories and microwave field effect transistors.
In European Patent Application EP-A-413491, a description is given of such a semiconductor device in the form of a semiconductor laser. The laser is built up of a number of layers of semiconducting material which contain InP or GaAs. One of said layers is the active layer which is bounded on both sides by, respectively, an n-type and a p-type cladding layer. One of said cladding layers carries a semiconducting contact or cap layer on which an insulating layer of silicon oxide is provided. Said insulating layer has one or more slit-shaped apertures on the inside of which a platinum electrode layer is in ohmic contact with the contact layer. The platinum layer extends over the insulating layer and is covered by a gold layer.
In the manufacture of such a semiconductor laser, use is made of a wafer of (mostly n-type) InP or GaAs on which the layers are provided by means of well-known techniques. Subsequently the wafer is cleaved (also termed dicing) to form laser chips. In this process the platinum layer may become completely or partly detached from the insulating layer, thereby rendering a part of the laser chips useless. In the above-mentioned Patent Application it is stated that a titanium layer having a thickness of 50 nm is located between the platinum layer and the silicon oxide layer. It is known per se that an intermediate layer of titanium may improve the adhesion of noble metals such as platinum to an oxidic substrate. Experiments carried out by Applicants have shown that in many cases the adhesion of a platinum layer to a silicon oxide surface, using an intermediate layer of titanium, is insufficient.